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<p>Following up on my earlier email. If there is a commitment to
checking in f18 already, feel free to disregard it. I went and
took a little bit closer look at the sources and want to share
some of the findings in case if anyone is interested. Disclosure:
I contribute to <a moz-do-not-send="true"
href="http://fort-compiler.org/">Fort</a> (fort-compiler.org),
which is the fork of the front-end David Greene mentioned.<br>
</p>
<p>From Stephen's announcement:<br>
<blockquote type="cite">
<p class="MsoNormal" style="caret-color: rgb(0, 0,
0);font-variant-caps: normal;orphans:
auto;text-align:start;widows: auto;-webkit-text-size-adjust:
auto;-webkit-text-stroke-width: 0px;word-spacing:0px"><span
style="color:black">At this point, we have documented and
implemented a healthy subset of the compiler for symbol
tables and scoping, name resolution, USE statements and
module files, constant representation, constant folding and
much of declaration, label and expression semantics. The
parser handles all of Fortran 2018 and OpenMP 4.5 and
implements a Fortran-aware preprocessor. The Fortran control
flow graph (CFG) is in review now. We continue to update
other documentation, such as the style guide and runtime
descriptor design.</span></p>
<span style="color:black"></span></blockquote>
Currently it looks like only the parser is <i>partially</i>
implemented in f18, there is no code generator (via LLVM or
otherwise) and, obviously, no object output. For that reason and
due to the condition of its test suite it is impossible to
reliably assess the state of Fortran 18 support (thought it does
look like a fair amount of effort went into it). State of OpenMP
support actually got me a bit puzzled, more on that below.<br>
</p>
<p>As I understand the announcement, f18 is intended to be used or
merged with Flang sources at some point, but that still does not
explain how it would integrate with LLVM, since Flang does not
seem invoke LLVM directly either (it used to produce LLVM IR as
text files). Because of this, it is likely that its code generator
component would have to be written from scratch. It is also
unclear if and how it would provide the library API which has been
announced.<br>
</p>
<p>A bit about the test suite -- I looked at the Fortran
(regression) part of it (as opposed to unit tests, which hopefully
are a relatively simple affair). Maybe nitpicking, but despite
"handles all of OpenMP 4.5" statement in the announcement there
seem to be only two references to OpenMP in tests. Most of the
regression tests are challenging to understand -- some list all
expected output upfront, some of the expected output is not
particularly human-friendly. Maybe I am used to Clang's test
suite, but it is unclear to me what each file is testing. Also,
regression testing relies on a set of shell scripts to do some of
the output checking.<br>
</p>
<p>My worry here that it would actually take years to develop f18
into an a working compiler, in which case there might be other
options worth considering for a Fortran front-end. In my opinion
(and this <i>may</i> be a matter of personal preference) a
healthier subset of the compiler would be more of an end-to-end
subset of it -- something that can be tested as a full product
while it is being developed. And then there is also the argument
for reusing Clang tooling, which David Greene keeps making, though
that idea does not seem to get a lot of interest.<br>
</p>
<p><br>
</p>
<p>Best,</p>
<p>Petr<br>
</p>
<div class="moz-cite-prefix">On 2/27/19 1:55 PM, Chris Lattner via
llvm-dev wrote:<br>
</div>
<blockquote type="cite"
cite="mid:27EDA52D-3E05-47A0-80FC-F2C635B0299F@nondot.org">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
On Feb 25, 2019, at 10:06 AM, Stephen Scalpone via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org" class=""
moz-do-not-send="true">llvm-dev@lists.llvm.org</a>> wrote:<br
class="">
<div>
<blockquote type="cite" class=""><span style="font-family:
Calibri, sans-serif; font-size: 12pt;" class="">We're
committed to developing LLVM's Fortran frontend for years to
come, and together with other members of the LLVM community
(e.g., ARM, US Dept of Energy) would like to do so as part
of the LLVM project.</span><br class="">
</blockquote>
<div><br class="">
</div>
<div>This is super exciting Stephen, congratulations to you and
everyone working on f18. I’m very excited to see this
happening and am thrilled about the approach you are taking.</div>
<div><br class="">
</div>
<blockquote type="cite" class="">
<div class="WordSection1" style="page: WordSection1;
caret-color: rgb(0, 0, 0); font-family: Helvetica;
font-size: 12px; font-style: normal; font-variant-caps:
normal; font-weight: normal; letter-spacing: normal;
text-align: start; text-indent: 0px; text-transform: none;
white-space: normal; word-spacing: 0px;
-webkit-text-stroke-width: 0px; text-decoration: none;">
<div style="margin: 0in 0in 0.0001pt; font-size: 12pt;
font-family: Calibri, sans-serif; caret-color: rgb(0, 0,
0); font-variant-caps: normal; text-align: start;
-webkit-text-stroke-width: 0px; word-spacing: 0px;"
class=""><span style="" class="">The f18 compiler source
code complies with most of LLVM's coding guidelines;
however, the code uses several C++17 features. We've
documented our use of C++17 here:<o:p class=""></o:p></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 12pt;
font-family: Calibri, sans-serif; caret-color: rgb(0, 0,
0); font-variant-caps: normal; text-align: start;
-webkit-text-stroke-width: 0px; word-spacing: 0px;"
class=""><span style="" class=""> <o:p class=""></o:p></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 12pt;
font-family: Calibri, sans-serif; caret-color: rgb(0, 0,
0); font-variant-caps: normal; text-align: start;
-webkit-text-stroke-width: 0px; word-spacing: 0px;"
class=""><span style="" class=""> <span
class="apple-converted-space"> </span><a
href="https://github.com/flang-compiler/f18/blob/master/documentation/C++17.md"
style="color: rgb(149, 79, 114); text-decoration:
underline;" class="" moz-do-not-send="true"><span
style="color: rgb(149, 79, 114);" class="">https://github.com/flang-compiler/f18/blob/master/documentation/C++17.md</span></a><o:p
class=""></o:p></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 12pt;
font-family: Calibri, sans-serif; caret-color: rgb(0, 0,
0); font-variant-caps: normal; text-align: start;
-webkit-text-stroke-width: 0px; word-spacing: 0px;"
class=""><br class="">
</div>
<div style="margin: 0in 0in 0.0001pt; font-size: 12pt;
font-family: Calibri, sans-serif; caret-color: rgb(0, 0,
0); font-variant-caps: normal; text-align: start;
-webkit-text-stroke-width: 0px; word-spacing: 0px;"
class=""><span style="" class="">Our request would be to
get a waiver for the C++11 requirement based on the fact
that we're skating to where the puck will be. In the
meantime, because F18 only exists as a stand-alone
program, early adopters would still have a useful parser
and analyzer for Fortran.<o:p class=""></o:p></span></div>
</div>
</blockquote>
<br class="">
</div>
<div>I personally see no problem or concerns with this at all.
This is a new project and the worst case is that f18 comes up
with some really cool stuff that the rest of the LLVM project
would love to share, but that can’t be done until it is
refactored to not use c++11. If/when that comes up, we can deal
with it on demand. I don’t see any particular reason to block
f18 from joining the project because of that speculative
concern.</div>
<div><br class="">
</div>
<div>-Chris</div>
<div><br class="">
</div>
<br class="">
<br>
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